mm/khugepaged: dedup and simplify hugepage alloc and charging

The following code is duplicated in collapse_huge_page() and
collapse_file():

        gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE;

	new_page = khugepaged_alloc_page(hpage, gfp, node);
        if (!new_page) {
                result = SCAN_ALLOC_HUGE_PAGE_FAIL;
                goto out;
        }

        if (unlikely(mem_cgroup_charge(page_folio(new_page), mm, gfp))) {
                result = SCAN_CGROUP_CHARGE_FAIL;
                goto out;
        }
        count_memcg_page_event(new_page, THP_COLLAPSE_ALLOC);

Also, "node" is passed as an argument to both collapse_huge_page() and
collapse_file() and obtained the same way, via
khugepaged_find_target_node().

Move all this into a new helper, alloc_charge_hpage(), and remove the
duplicate code from collapse_huge_page() and collapse_file().  Also,
simplify khugepaged_alloc_page() by returning a bool indicating allocation
success instead of a copy of the allocated struct page *.

Link: https://lkml.kernel.org/r/20220706235936.2197195-5-zokeefe@google.com
Signed-off-by: Zach O'Keefe <zokeefe@google.com>
Suggested-by: Peter Xu <peterx@redhat.com>
Acked-by: David Rientjes <rientjes@google.com>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Cc: Alex Shi <alex.shi@linux.alibaba.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Axel Rasmussen <axelrasmussen@google.com>
Cc: Chris Kennelly <ckennelly@google.com>
Cc: Chris Zankel <chris@zankel.net>
Cc: David Hildenbrand <david@redhat.com>
Cc: Helge Deller <deller@gmx.de>
Cc: Hugh Dickins <hughd@google.com>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Pasha Tatashin <pasha.tatashin@soleen.com>
Cc: Pavel Begunkov <asml.silence@gmail.com>
Cc: Rongwei Wang <rongwei.wang@linux.alibaba.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Song Liu <songliubraving@fb.com>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Zi Yan <ziy@nvidia.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: "Souptick Joarder (HPE)" <jrdr.linux@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: zokeefe

mm/khugepaged.c

@@ -813,19 +813,18 @@ static int khugepaged_find_target_node(struct collapse_control *cc)
 }
 #endif
 
-static struct page *
-khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node)
+static bool khugepaged_alloc_page(struct page **hpage, gfp_t gfp, int node)
 {
 	*hpage = __alloc_pages_node(node, gfp, HPAGE_PMD_ORDER);
 	if (unlikely(!*hpage)) {
 		count_vm_event(THP_COLLAPSE_ALLOC_FAILED);
 		*hpage = ERR_PTR(-ENOMEM);
-		return NULL;
+		return false;
 	}
 
 	prep_transhuge_page(*hpage);
 	count_vm_event(THP_COLLAPSE_ALLOC);
-	return *hpage;
+	return true;
 }
 
 /*
@@ -923,10 +922,24 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm,
 	return true;
 }
 
-static void collapse_huge_page(struct mm_struct *mm,
-				   unsigned long address,
-				   struct page **hpage,
-				   int node, int referenced, int unmapped)
+static int alloc_charge_hpage(struct page **hpage, struct mm_struct *mm,
+			      struct collapse_control *cc)
+{
+	/* Only allocate from the target node */
+	gfp_t gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE;
+	int node = khugepaged_find_target_node(cc);
+
+	if (!khugepaged_alloc_page(hpage, gfp, node))
+		return SCAN_ALLOC_HUGE_PAGE_FAIL;
+	if (unlikely(mem_cgroup_charge(page_folio(*hpage), mm, gfp)))
+		return SCAN_CGROUP_CHARGE_FAIL;
+	count_memcg_page_event(*hpage, THP_COLLAPSE_ALLOC);
+	return SCAN_SUCCEED;
+}
+
+static void collapse_huge_page(struct mm_struct *mm, unsigned long address,
+			       struct page **hpage, int referenced,
+			       int unmapped, struct collapse_control *cc)
 {
 	LIST_HEAD(compound_pagelist);
 	pmd_t *pmd, _pmd;
@@ -937,31 +950,22 @@ static void collapse_huge_page(struct mm_struct *mm,
 	int isolated = 0, result = 0;
 	struct vm_area_struct *vma;
 	struct mmu_notifier_range range;
-	gfp_t gfp;
 
 	VM_BUG_ON(address & ~HPAGE_PMD_MASK);
 
-	/* Only allocate from the target node */
-	gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE;
-
 	/*
 	 * Before allocating the hugepage, release the mmap_lock read lock.
 	 * The allocation can take potentially a long time if it involves
 	 * sync compaction, and we do not need to hold the mmap_lock during
 	 * that. We will recheck the vma after taking it again in write mode.
 	 */
 	mmap_read_unlock(mm);
-	new_page = khugepaged_alloc_page(hpage, gfp, node);
-	if (!new_page) {
-		result = SCAN_ALLOC_HUGE_PAGE_FAIL;
-		goto out_nolock;
-	}
 
-	if (unlikely(mem_cgroup_charge(page_folio(new_page), mm, gfp))) {
-		result = SCAN_CGROUP_CHARGE_FAIL;
+	result = alloc_charge_hpage(hpage, mm, cc);
+	if (result != SCAN_SUCCEED)
 		goto out_nolock;
-	}
-	count_memcg_page_event(new_page, THP_COLLAPSE_ALLOC);
+
+	new_page = *hpage;
 
 	mmap_read_lock(mm);
 	result = hugepage_vma_revalidate(mm, address, &vma);
@@ -1235,10 +1239,9 @@ static int khugepaged_scan_pmd(struct mm_struct *mm, struct vm_area_struct *vma,
 out_unmap:
 	pte_unmap_unlock(pte, ptl);
 	if (ret) {
-		node = khugepaged_find_target_node(cc);
 		/* collapse_huge_page will return with the mmap_lock released */
-		collapse_huge_page(mm, address, hpage, node,
-				referenced, unmapped);
+		collapse_huge_page(mm, address, hpage, referenced, unmapped,
+				   cc);
 	}
 out:
 	trace_mm_khugepaged_scan_pmd(mm, page, writable, referenced,
@@ -1506,7 +1509,7 @@ static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
  * @file: file that collapse on
  * @start: collapse start address
  * @hpage: new allocated huge page for collapse
- * @node: appointed node the new huge page allocate from
+ * @cc: collapse context and scratchpad
  *
  * Basic scheme is simple, details are more complex:
  *  - allocate and lock a new huge page;
@@ -1523,12 +1526,11 @@ static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
  *    + restore gaps in the page cache;
  *    + unlock and free huge page;
  */
-static void collapse_file(struct mm_struct *mm,
-		struct file *file, pgoff_t start,
-		struct page **hpage, int node)
+static void collapse_file(struct mm_struct *mm, struct file *file,
+			  pgoff_t start, struct page **hpage,
+			  struct collapse_control *cc)
 {
 	struct address_space *mapping = file->f_mapping;
-	gfp_t gfp;
 	struct page *new_page;
 	pgoff_t index, end = start + HPAGE_PMD_NR;
 	LIST_HEAD(pagelist);
@@ -1540,20 +1542,11 @@ static void collapse_file(struct mm_struct *mm,
 	VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem);
 	VM_BUG_ON(start & (HPAGE_PMD_NR - 1));
 
-	/* Only allocate from the target node */
-	gfp = alloc_hugepage_khugepaged_gfpmask() | __GFP_THISNODE;
-
-	new_page = khugepaged_alloc_page(hpage, gfp, node);
-	if (!new_page) {
-		result = SCAN_ALLOC_HUGE_PAGE_FAIL;
+	result = alloc_charge_hpage(hpage, mm, cc);
+	if (result != SCAN_SUCCEED)
 		goto out;
-	}
 
-	if (unlikely(mem_cgroup_charge(page_folio(new_page), mm, gfp))) {
-		result = SCAN_CGROUP_CHARGE_FAIL;
-		goto out;
-	}
-	count_memcg_page_event(new_page, THP_COLLAPSE_ALLOC);
+	new_page = *hpage;
 
 	/*
 	 * Ensure we have slots for all the pages in the range.  This is
@@ -1965,8 +1958,7 @@ static void khugepaged_scan_file(struct mm_struct *mm, struct file *file,
 			result = SCAN_EXCEED_NONE_PTE;
 			count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
 		} else {
-			node = khugepaged_find_target_node(cc);
-			collapse_file(mm, file, start, hpage, node);
+			collapse_file(mm, file, start, hpage, cc);
 		}
 	}